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topic 5807

Chrome Plating and Fatigue Life


(2000)

I am looking for research on plating and fatigue life. We have found in the aluminum wheel industry, that chrome wheels have a lower fatigue life compared to painted wheels. The reason, I have heard, is the additional shear stresses induced by the plating itself. I have also heard that plating is in a state of tension or compression which results in residual stresses on the substrate. However, I have not seen any quantification or a method to quantify of this stress. If anyone has done any work or has any insight into this matter, I would really appreciate it.

Bobby Sohi
- Mason,Ohio,US


(2000)

I am also investigating fatigue life debit for Ti-6Al-4V actuator cylinders used for aerospace applications. However, we are plating with an electroless nickel process. The coating is on the inside diameter of a 2-inch bore.

Keep in mind, the internal stresses you mentioned in the plating are often relieved by forming networks of cracks. In our case, it is beleived the nickel plating has an amorphous crystal structure with essentially no ductility and is therefore prone to brittle cracking, particularly since we precipitation harden it to rockwell-C levels similar to chrome. I have verified the cracks go through to the substrate on my SEM at work. Not only do the internal stresses accentuate fatigue crack initiation, they act as stress concentrations, or fatigue crack origins. Also, the intrinsic fatigue properties of the plating (in our case nickel) are a factor in the as-plated structure.

I profess to be no expert in this subject but have much practical experience if you would like to discuss further.

Terence Savas
Parker Aerospace - Mission Viejo, CA USA



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